The human spinal cord and brain are covered with the meninges membranes, consisting of three overlapping layers of tissue including the outermost dura mater, arachnoid mater and innermost pia mater. The meningeal membranes are critical to the operation of the central nervous system and their disruption, by accident or surgical intervention, can cause serious consequences unless repaired. Dural tears are common complications in spine surgery and can range in size from nonleaking pinholes to large defects that require tissue reconstruction with a patch. A persistent tear can lead to severe headaches, CSF fistula, formation of a pseudocyst, nerve root entrapment and fluid collection. Large retrospective series have reported an incidence of 1% for cervical surgeries (Hannallah D, Lee J, Khan M, Donaldson W F, Kang J D: Cerebrospinal fluid leaks following cervical spine surgery. J Bone Joint Surg Am 2008; 90(5):1101-1105), and 7.6% and 15.9%, respectively, for primary lumbar and revision lumbar surgeries (Khan M H, Rihn J, Steele G, et al: Postoperative management protocol for incidental dural tears during degenerative lumbar spine surgery: A review of 3,183 consecutive degenerative lumbar cases. Spine (Phila Pa. 1976) 2006:31(22):2609-2613).
A watertight closure is the critical factor in repairing the tear. Direct suture repair is routinely used to repair dural tears, but leakage through suture holes can occur. Autologous fat grafts harvested through the same incision have been used to form a hydrophobic seal to prevent leakage. The graft should be sufficiently large to cover the dura and is sutured to the dura adjacent to the defect (Mayfield F H, Kurokawa K: Watertight closure of spinal dura mater: Technical note. J Neurosurg 1975;43(5):639-640). Muscle and fascia have also been used as patches. The use of autologous tissues, however, can lead to prolonged operating time, blood loss and separate incisions. In addition, the quantity of autologous graft may be inadequate in children. Xenografts and cross-linked animal-derived collagen matrices can be used as dural patches, but carry the risk of disease transmission.
Adjunct techniques to assist in sealing the dural tear include fibrin glue and hydrogels. Fibrin glue is prepared from pooled blood and has the potential to transmit disease. At this time, the application of fibrin glue to seal dural tears constitutes off label use. Synthetic hydrogels such as the DuraSeal Spine Sealant System (Confluent Surgical Inc., Waltham, Mass.) consist of two components (polyethylene glycol ester and trilysine amine) and a delivery system which polymerize at the defect site to form a seal. As the hydrogel swells to up to 50% in size during polymerization, neural compression may occur.
Post-operative fibrosis, also referred to as scar tissue formation or post-operative adhesion, is a natural occurrence following various surgical procedures. This natural wound healing cascade in most instances results in the formation of soft tissue adhesions, which either tether, compress, or effect surgical accessibility. Fibrosis is particularly problematic in post-surgical procedures of the spine. For example, peridural fibrosis is the fibroblastic invasion of the nerve roots and peridural sac that are exposed during surgery. The scar tissue can engulf the dura and nerve roots, which can ultimately result in the reoccurrence of symptoms similar to those experienced prior to surgery. Thus, subsequent operations to address the problem may have to be performed, which provides additional inconvenience, costs, and risks to the patient.
Scar formation after spinal surgery can be prevented by the use of membranes and foams applied directly to the spine. Currently, membranes used for adhesion prevention are derived from synthetic type I, II, and III collagen, acellular dermal matrix allograft, HA cellulose film or porcine intestinal submucosa (SIS). These materials possess a variety of disadvantages including poor handling characteristics, undesirable resorption profile, limited fixation capabilities, and limited storage options. Thus, what is needed are grafts that exhibit good adhesion to body tissues and facilitate wound healing yet that do not possess the disadvantages of commercially available options.